Lightweight well cement compositions and methods

ABSTRACT

Lightweight cement compositions and methods of cementing a subterranean zone penetrated by a well bore utilizing the compositions are provided. A lightweight cement composition of the invention is basically comprised of a coarse particulate hydraulic cement, an ultrafine particulate hydraulic cement mixture comprised of slag cement and a Portland or equivalent cement, fly ash, fumed silica, hollow glass spheres and water.

This application is a Divisional of application Ser. No. 10/086,024filed on Feb. 28, 2002, now U.S. Pat. No. 6,562,122 which is aContinuation of application Ser. No. 09/664,487 filed on Sep. 18, 2000,abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to lightweight well cement compositionsand methods of cementing subterranean zones penetrated by well boresusing the compositions.

2. Description of the Prior Art

In carrying out completion operations in oil, gas and water wells,hydraulic cement compositions are commonly utilized. For example,hydraulic cement compositions are used in primary cementing operationswhereby pipe is cemented in the well bore. That is, a hydraulic cementcomposition is pumped into the annular space between the walls of thewell bore and the exterior of a pipe disposed therein. The cementcomposition is permitted to set in the annular space thereby forming anannular sheath of hardened impermeable cement therein. The objective ofthe cement sheath is to physically support and position the pipe in thewell bore and bond the pipe to the walls of the well bore whereby theundesirable migration of fluids between zones or formations penetratedby the well bore is prevented.

Recently the need for better economics, higher productivity, environmentprotection and more efficient well operations has brought about new welldrilling and completing techniques. Examples of such new techniquesinclude the reduction of the well bore diameter (referred to as a slimhole) and extending the reservoir penetration by drilling small lateralwell bores which are completed using small diameter pipe such as coiledtubing to increase the productivity of the reservoir. The performance ofprimary cementing operations in the smaller annular spaces in the wellbores requires improved lightweight cement compositions having lowviscosities so that the cement compositions can be accurately placed. Inaddition, the cement compositions must have good static gel strength,low rheology, high compressive strength, low fluid loss, lowpermeability, good chemical resistance and a broad operating temperaturerange. That is, the cement compositions must be suitable for use attemperatures in the range of from about 45° F. to 270° F.

Thus, there are needs for improved lightweight cement compositions andmethods of using the compositions for cementing pipe in well bores.

SUMMARY OF THE INVENTION

The present invention provides improved lightweight cement compositionsand methods of cementing subterranean zones utilizing the compositionswhich meet the needs described above and overcome the deficiencies ofthe prior art. The lightweight cement compositions of the invention arebasically comprised of a coarse particulate hydraulic cement; anultrafine particulate hydraulic cement mixture comprised of slag cementand a Portland or equivalent cement present in an amount in the range offrom about 50% to about 150% by weight of the coarse particulatehydraulic cement in the composition; fly ash present in an amount in therange of from about 50% to about 150% by weight of the coarseparticulate hydraulic cement in the composition; fumed silica present inan amount in the range of from about 20% to about 60% by weight of thecoarse particulate hydraulic cement in the composition; hollow glassspheres present in an amount sufficient to impart a density to thecement composition in the range of from about 9 to about 13 pounds pergallon; and water present in an amount sufficient to form a slurry. Thecement compositions also preferably include a fluid loss controladditive present in an amount in the range of from about 0.2% to about8% by weight of the coarse particulate hydraulic cement in thecomposition.

The coarse particulate hydraulic cement has a particle size no greaterthan about 118 microns and a specific surface area no less than about2800 square centimeters per gram. The slag cement and Portland orequivalent cement in the ultrafine cement mixture has a particle size nogreater than about 30 microns, a mean particle size of 6 microns and aspecific surface area no less than about 6000 centimeters per gram.

The methods of the present invention for cementing a subterranean zonepenetrated by a well bore are comprised of the following steps. Alightweight cement composition of the invention is prepared comprised ofa coarse particulate hydraulic cement, an ultrafine particulatehydraulic cement mixture of slag cement and Portland or equivalentcement, fly ash, fumed silica, hollow glass spheres, sufficient water toform a slurry and optionally, a fluid loss control additive. Afterpreparation, the cement composition is placed in the subterranean zoneto be cemented and the cement composition is allowed to set into a hardimpermeable mass.

When the subterranean zone to be cemented has a temperature in the rangeof from about 45° F. to about 100° F., a cement composition setaccelerator is included in the cement composition. When the subterraneanzone has a temperature in the range of from about 100° F. to about 270°F., a set accelerator and a dispersing agent are included in the cementcomposition. When the subterranean zone has a temperature in the rangeof from about 230° F. to about 270° F., a cement composition setretarder and silica flour are included in the cement composition. Thesilica flour functions to prevent set cement strength retrogression.

It is, therefore, an object of the present invention to provide improvedlightweight well cementing compositions and methods.

Other and further objects, features and advantages of the presentinvention will be readily apparent to those skilled in the art upon areading of the description of preferred embodiments which follows.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention provides universal non-foamed lightweight cementcompositions and methods of using the compositions for cementingsubterranean zones penetrated by well bores. The lightweight cementcompositions can be used over a broad temperature range, i.e., fromabout 45° F. to about 270° F. at densities in the range of from about 9to about 13 pounds per gallon. The cement compositions have excellentproperties including high static gel strengths, low rheologies, lowfluid loss, high compressive strength upon setting, low permeabilityupon setting and resistance to chemical deterioration and failure due tosulfate degradation or the like.

The lightweight cement compositions of this invention are basicallycomprised of a coarse particulate hydraulic cement; an ultrafineparticulate hydraulic cement mixture comprised of slag cement and aPortland or equivalent cement, fly ash, fumed silica, hollow glassspheres, water present in an amount sufficient to form a slurry andoptionally, a fluid loss control additive.

The coarse particulate hydraulic cement can be any of a variety ofhydraulic cements having a maximum particle size of about 118 micronsand a specific surface area of about 2800 square centimeters per gram.Portland cement is generally preferred, and the coarse cement can be,for example, one or more of the various Portland cements designated asAPI Classes A-H cements. These cements are identified and defined in theAPI Specification For Materials And Testing For Well Cements, APISpecification 10, 5^(th) Edition, dated Jul. 1, 1990 of the AmericanPetroleum Institute. API Portland cements generally have a maximumparticle size of about 90 microns and a specific surface of about 3900square centimeters per gram. When an API Portland cement is utilized asthe coarse hydraulic cement in accordance with this invention, it ispreferably API Class G cement. Other hydraulic cements which are morecoarse than API Portland cement can also be used up to the maximumparticle size set forth above. When more coarse cements are used, theypreferably have properties which are the same or similar as API Class Gcement.

The ultrafine particulate hydraulic cement mixture comprised of slagcement and a Portland or equivalent cement has a particle size nogreater than about 30 microns, a mean particle size of 6 microns and aspecific surface area no less than about 6,000 centimeters per gram.Preferably the ultrafine particulate hydraulic cement mixture has aparticle size no greater than about 17 microns and a specific surfacearea no less than about 7,000 centimeters per gram, and more preferably,a particle size no greater than about 11 microns and a specific surfacearea no less than about 10,000 centimeters per gram. Ultrafineparticulate hydraulic cement mixtures of slag cement and Portland orequivalent cement having particle sizes and specific surface areas asdescribed above are disclosed in U.S. Pat. No. 4,761,183 issued on Aug.2, 1988 to Clarke which is incorporated herein by reference. Thepreferred ultrafine cement mixture for use in accordance with thisinvention is comprised of slag cement and Portland or equivalent cementwherein the slag cement is present in the mixture in an amount of atleast about 50% by weight of the mixture. The slag cement is morepreferably included in the ultrafine cement mixture in an amount ofabout 65% by weight of the mixture and most preferably in an amount ofabout 75% by weight of the mixture.

The ultrafine particulate hydraulic cement mixture as described above incombination with the coarse particulate hydraulic cement provides highcompressive strengths to the set cement compositions of this invention.The ultrafine particulate hydraulic cement mixture is included in thelightweight cement composition of this invention in an amount in therange of from about 50% to about 150% by weight of the coarseparticulate hydraulic cement in the composition.

The fly ash utilized in the lightweight cement compositions of thisinvention is preferably ASTM Class F fly ash. The fly ash functions as alightweight filler in the cement compositions and in combination withthe coarse particulate hydraulic cement provides low permeability to thecement compositions upon setting. The fly ash is included in the cementcompositions in an amount in the range of from about 50% to about 150%by weight of the coarse particulate hydraulic cement in the composition.

The fumed silica provides thickening and thixotropic properties to thecement compositions. The fumed silica is included in the cementcompositions in an amount in the range of from about 20% to about 60% byweight of the coarse particulate hydraulic cement therein.

The hollow glass spheres are included in the cement compositions of thisinvention to make them lightweight, i.e., to provide low densities tothe compositions. Particularly suitable such hollow glass spheres arecommercially available from Halliburton Energy Services, Inc. of Duncan,Okla., under the trade designation “SILICALITE™.” The hollow glassspheres are included in the cement compositions of this invention in anamount in the range of from about 21% to about 310% by weight of thecoarse particulate hydraulic cement therein to provide densities to thecement compositions in the range of from about 9 to about 13 pounds pergallon.

The water in the cement compositions of this invention can be freshwater, unsaturated salt solutions or saturated salt solutions includingbrine and seawater. The water is included in the cement composition inan amount sufficient to form a pumpable slurry, i.e., an amount in therange of from about 128% to about 400% by weight of the coarseparticulate hydraulic cement in the compositions.

The cement compositions of this invention also preferably include afluid loss control additive. While a variety of fluid loss controladditives can be utilized, a preferred fluid loss control additive iscomprised of a mixture of a graft copolymer having a backbone of lignin,lignite or salts thereof and a grafted pendant group of2-acrylamido-2-methylpropanesulfonic acid and a copolymer or copolymersalt of N,N-dimethylacrylamide and 2-acrylamido-2-methyl propanesulfonic acid. The above described graft copolymer is disclosed in U.S.Pat. No. 4,676,317 issued to Fry et al. on Jun. 30, 1987 and the abovedescribed copolymer or copolymer salt is disclosed in U.S. Pat. No.4,555,269 issued to Rao et al. on Nov. 26, 1985, both of which areincorporated herein by reference. The mixture of the above fluid losscontrol additives provides a synergistic increase in fluid loss controland brings about less settling and less free water. When used, the fluidloss control additive is included in the cement compositions of thisinvention in an amount in the range of from about 0.2% to about 8% byweight of the coarse particulate hydraulic cement in the compositions.

As mentioned, the lightweight cement compositions of this invention canbe utilized over a broad temperature range of from about 45° F. to about270° F. The density of the cement compositions can be varied by varyingthe amounts of the hollow glass spheres included in the compositions.That is, the lightweight compositions of this invention can have adensity from about 9 to about 13 pounds per gallon. The ability to varythe density is important in cementing subterranean zones in that lowdensity cement compositions often must be used to prevent fracturing ofthe subterranean zones and lost circulation from taking place. Thecement compositions of this invention have low rheologies whereby whenrequired they can be pumped at turbulent flow. Pumping the cementcomposition at turbulent flow aids in displacing drilling fluid from thewell bore. The low rheology of the cement composition also produces lowfriction pressure when the composition is pumped which lowers the riskof fracturing easily fractured zones or formations. When the cementcompositions of this invention are utilized in the above mentioned slimhole completions, low rheology is particularly important in preventingfracturing of weak subterranean zones or formations.

When the cement composition of this invention is used in low temperatureapplications, i.e., applications where the zone being cemented has atemperature in the range of from about 45° F. to about 100° F., a cementcomposition set accelerator and a cement composition dispersing agentare preferably included in the composition. As will be understood bythose skilled in the art, the set accelerator shortens the time requiredfor the cement composition to set at the low temperatures involved andthe dispersing agent lowers the rheology of the cement composition.

While a variety of cement composition set accelerators can be utilized,calcium chloride is presently preferred. When used, the set acceleratoris included in the cement composition in an amount in the range of fromabout 1% to about 12% by weight of the coarse particulate hydrauliccement therein.

A variety of dispersing agents can also be utilized in accordance withthis invention. A particularly suitable such dispersing agent is thecondensation product of acetone, formaldehyde and sodium sulfite. Such adispersing agent is commercially available from Halliburton EnergyServices, Inc. of Duncan, Okla., under the tradename “CFR-3™.” Thedispersing agent utilized is included in the cement composition in anamount in the range of from about 0.2% to about 8% by weight of thecoarse particulate hydraulic cement in the composition.

When the temperature of the subterranean zone to be cemented is in therange of from about 100° F. to about 230° F., the above described cementcomposition set accelerator is preferably included therein.

When the subterranean zone or formation to be cemented has a temperaturein the range of from about 230° F. to about 270° F., the above describedcement composition preferably includes a cement composition set retarderand silica flour to prevent set cement strength retrogression. Whilevarious set retarders can be utilized, the set retarder used inaccordance with this invention is preferably a copolymer of2-acrylamido-2-methylpropanesulfonic acid and acrylic acid attemperatures up to 250° F. or a copolymer of2-acrylamdio-2-methylpropane sulfonic acid and itaconic acid attemperatures above 250° F. Such set retarders are commercially availableunder the trade designations “SCR-100™” and “SCR-500™,” respectively,from Halliburton Energy Services, Inc. of Duncan, Okla. The set retarderfunctions to delay the set of the cement composition until it has beenplaced in the subterranean zone to be cemented. The amount of setretarder utilized increases with increasing temperature and is generallyincluded in the cement compositions of this invention in an amount inthe range of from about 0.2% to about 8% by weight of the coarseparticulate hydraulic cement in the compositions.

As indicated above, silica flour is included in the cement compositionsto prevent the compressive strength of the set cement from decreasingover time due to the high temperature of the subterranean zone in whichit is placed. When used, the silica flour is included in the cementcompositions in an amount in the range of from about 20% to about 60% byweight of the coarse particulate hydraulic cement in the compositions.

In order to prevent the chemical degradation of the set cementcomposition of this invention, the coarse particulate hydraulic cementutilized can optionally be an API Class G Portland cement which does notcontain tricalcium aluminate. The presence of tricalcium aluminate inthe cement can cause sulfate degradation of the cement.

A particularly suitable lightweight cement composition of this inventionis comprised of a coarse particulate API Class G Portland cement havinga particle size no greater than about 118 microns and a specific surfacearea no less than about 2800 square centimeters per gram; an ultrafineparticulate hydraulic cement mixture comprised of slag cement and aPortland or equivalent cement, the cement mixture having a particle sizeno greater than about 30 microns and a specific surface area no lessthan about 6,000 centimeters per gram and being present in an amount inthe range of from about 50% to about 150% by weight of the coarseparticulate hydraulic cement in the composition; ASTM Class F fly ash orthe equivalent present in an amount in the range of from about 50% toabout 150% by weight of the coarse particulate hydraulic cement in thecomposition; fumed silica present in an amount in the range of fromabout 20% to about 60% by weight of the coarse particulate hydrauliccement in the composition; hollow glass spheres present in an amountsufficient to impart a density to the cement composition in the range offrom about 9 to about 13 pounds per gallon; and water present in anamount sufficient to form a slurry.

The water in the composition can be selected from the group consistingof fresh water, saturated salt solutions and unsaturated salt solutionsincluding brine and seawater, and the water can be present in a generalamount in the range of from about 128% to about 400% by weight of thecoarse particulate hydraulic cement in the composition.

As indicated above, the composition preferably also includes a fluidloss control additive comprised of a mixture of the graft copolymer(Halliburton “SCR-100™”) and the copolymer or copolymer salt(Halliburton “SCR-500™”) described above in an amount in the range offrom about 0.2% to about 8% by weight of the coarse particulatehydraulic cement in the composition.

Further, as also described above, depending on the temperature of thesubterranean zone to be cemented, one or more additional additives arepreferably included in the cement compositions of this invention. Theadditives include, but are not limited to, a cement composition setaccelerator, a cement composition dispersing agent, a cement compositionset retarder and silica flour for preventing set cement strengthretrogression at elevated temperatures.

The methods of cementing a subterranean zone penetrated by a well borein accordance with the present invention are basically comprised of thefollowing steps. A lightweight cement composition of this inventionbasically comprised of a coarse particulate hydraulic cement, anultrafine particulate hydraulic cement mixture of slag cement and aPortland or equivalent cement, fly ash, fumed silica, hollow glassspheres and sufficient water to form a slurry is prepared. Thereafter,the cement composition is placed in the subterranean zone to be cementedand the cement composition is allowed to set into a hard impermeablemass.

In order to further illustrate the lightweight cement compositions andmethods of the present invention, the following examples are given.

EXAMPLE 1

A lightweight cement composition of the present invention was preparedcomprising coarse particulate API Class G Portland cement (Dyckerhoff),an ultrafine particulate hydraulic cement mixture comprised of 75% byweight slag cement and 25% by weight of Portland or equivalent cement,ASTM Class F fly ash, fumed silica, hollow glass spheres, fresh waterand a mixture of two fluid loss control agents, i.e., a graft polymer oflignin, lignite or their salts and a grafted pendant group comprised of2-acrylamido-2-methylpropane sulfonic acid and a copolymer or copolymersalt of N,N-dimethylacrylamide and 2-acrylamido-2-methylpropane sulfonicacid. Test samples of the cement compositions were tested for density,thickening time, rheology, zero gel time and transition time inaccordance with the procedures set forth in the above mentioned APISpecification 10. In addition, the compressive strength of the cementcomposition after setting was determined. All of the above listed testswere performed at 45° F. The amounts of the components of the testcement composition as well as the test results are given in Table Ibelow.

TABLE I Cement Composition Properties At 45° F. Quantity, ThickeningCompressive Strength¹ Zero Test % by wt. Time To 100 Time To Time ToAfter Gel Transition Composition of Coarse Density, Bc at 45° F.,Rheology 50 psi, 500 psi, 66 Hrs, Time, Time, Components Cement lb/galHrs:min 300-200-100-60-30-6-3 Hrs:min Hrs:min psi Hrs:min Hrs:minPortland Class G coarse cement² Ultrafine Cement³ 100 Fly Ash⁴ 100 FumedSilica 40 Hollow Glass Spheres 60 12.5 7:54 205-143-57-61-57-12-8 14:1836:57 976 4:01 0:46 Water 161 CaCl₂ 9.6 Fluid Loss 3.6 Control Additive⁵Dispersant⁶ 0.6 ¹Ultrasonic Cement Analyzer ²Dyckerhoff cement ³75% slagcement - 25% Portland cement ⁴ASTM Class F fly ash ⁵Mixture of graftcopolymer (U.S. Pat. No. 4,676,317) and copolymer or copolymer salt(U.S. Pat. No. 4,555,269) ⁶Condensation product of acetone, formaldehydeand sodium sulfite

From Table I, it can be seen that the cement composition of thisinvention had excellent properties at 45° F.

EXAMPLE 2

A lightweight cement composition of this invention was preparedcomprised of a coarse particulate API Class G Portland cement(Dyckerhoff), an ultrafine particulate hydraulic cement mixturecomprised of slag cement and a Portland or equivalent cement, ASTM ClassF fly ash, fumed silica, hollow glass spheres, fresh water, a cement setaccelerator comprised of calcium chloride and a mixture of two fluidloss control additives, i.e., a graft polymer comprised of lignin,lignite or their salts and a grafted pendant group comprising2-acrylamido-2-methylpropane sulfonic acid and a copolymer or copolymersalt of N,N-dimethylacrylamide and 2-acrylamido-2-methylpropane sulfonicacid. Test portions of the cement composition were tested for density,thickening time, rheology, fluid loss, and free water in accordance withthe procedures set forth in the above mentioned API Specification 10. Inaddition, the compressive strength of the cement composition wasdetermined. All of the above mentioned tests were determined at 100° F.The amounts of the various components in the cement composition testedas well as the test results are set forth in Table II below.

TABLE II Cement Composition Properties At 100° F. Quantity, ThickeningFluid Spec. Compressive Strength,¹ Test % by wt. Time To Loss, FreeGravity, Time to Time to After Composition of Coarse Density, 70 Bc, 100Bc, Rheology cc/30 Water, top/ 50 psi, 500 psi, 24 Final, ComponentsCement lb/gal Hrs:min Hrs:min 300-200-100-60-30-6-3 min % bottom Hrs:minHrs:min Hrs psi/hrs Portland Class G Coarse Cement² Ultrafine Cement³100 Fly Ash⁴ 100 Fumed Silica 40 11.66 2:55 2:56 56-41-23-14-8-3-2.5 440 1.331/ 7:34 10:53 1816 2839/68 1.561 Hollow Glass 60 Spheres Water 262CaCl₂ 12 Fluid Loss Control 3.6 Additive⁵ ¹Ultrasonic Cement Analyzer²Dyckerhoff cement ³75% slag cement - 25% Portland cement ⁴ASTM Class Ffly ash ⁵Mixture of graft copolymer (U.S. Pat. No. 4,676,317) andcopolymer or copolymer salt (U.S. Pat. No. 4,555,269) ⁶Condensationproduct of acetone, formaldehyde and sodium sulfite

From Table II it can be seen that the tested cement composition of thisinvention had excellent properties at 100° F.

EXAMPLE 3

Five test cement compositions of the present invention were preparedcontaining various amounts of a coarse particulate API Class G Portlandcement (Dyckerhoff), an ultrafine particulate hydraulic cement mixturecomprised of slag cement and a Portland or equivalent cement, fly ash,fumed silica, hollow glass spheres, fresh water, silica flour, a mixtureof two fluid loss control additives, i.e., a graft polymer comprised oflignin, lignite or their salts and a grafted pendant group comprised of2-acrylamido-2-methylpropane sulfonic acid and a copolymer ofN,N-dimethylacrylamide and 2-acrylamido-2-methylpropane sulfonic acid;and a set retarder selected from a copolymer of2-acrylamido-2-methylpropane sulfonic acid and acrylic acid or acopolymer of 2-acrylamido-2-methylpropane sulfonic acid and itaconicacid. Test samples of each composition were tested for density,thickening time, rheology, fluid loss and free water in accordance withthe procedure set forth in the above mentioned API Specification 10. Thecompressive strengths of set portions of the cement compositions werealso determined. All of the tests were run at temperatures in the rangeof from 200° F. to 270° F. The amounts of the test cement compositioncomponents and the test results are set forth in Table III below.

TABLE III Cement Composition Properties At 200° F. To 270° F. TestComposition No. 1 2 3 4 5 Test Composition Components, % by wt. CoarseCement Portland Class G Coarse Cement² Ultrafine Cement³ 100 100 100 100100 Fly Ash⁴ 100 100 100 100 100 Fumed Silica 40 40 40 40 40 HollowGlass 60 60 60 60 60 Spheres Water 264 264 264 264 264 Fluid LossControl 6.10 6.10 6.10 5.10 5.10 Additive⁵ Set Retarder⁶ 1.32 2.2 2.2 00 Set Retarder⁷ 0 0 0 2.34 2.34 Silica Flour⁸ 0 0 0 0 0 Density. lb/gal11.66 11.66 11.66 11.66 11.66 Thickening Time To: Temperature, ° F. 200240 260 270 270 70 Bc, Hrs:min 3:30 5:37 — 3:22 3:10 100 Bc, Hrs:min3:32 5:40 4:04 3:23 3:11 Rheology at 195° F. 300 175 93 80 120 70 200112 52 49 78 45 100 63 26 27 40 24  60 42 17 17 26 15  30 25 9 9 15 7  6 8 3 3 4 1   3 6 2 2 3 1 Fluid Loss at 195° F. cc/30 min 34 34 36 36 51Free Water, % 0 0 0 0 0 Compressive Strength¹ Temperature, ° F. 200 240260 270 270 Time to 50 psi, 7:09 6:50 4:45 2:41 — Hrs:min Time to 500psi, 8:13 9:21 6:16 6:43 8:32 Hrs:min After 24 hours, psi 2400 1200 1531700 1105 psi/days 2639/90 1465/2 1534/2 1877/84 1556/4 psi/days — —1901/— 1600/112 1850/120 ¹Ultrasonic Cement Analyzer ²Dyckerhoff cement³75% slag - 25% Portland cement ⁴ASTM Class F fly ash ⁵Mixture of graftcopolymer (U.S. Pat. No. 4,676,317) and copolymer or copolymer salt(U.S. Pat. No. 4,555,269) ⁶Copolymer of2-acrylamido-2-methylpropanesulfonic acid and acrylic acid. ⁷Copolymerof 2-acrylamido-2-methylpropanesulfonic acid and itaconic acid.⁸Prevents set cement compressive strength retrogression.

From Table III, it can be seen that the lightweight cement compositionsof the present invention have excellent properties at temperatures inthe range of from 200° F. to 275° F.

Thus, the present invention is well adapted to carry out the objects andattain the ends and advantages mentioned as well as those which areinherent therein. While numerous changes may be made by those skilled inthe art, such changes are encompassed within the spirit of thisinvention as defined by the appended claims.

What is claimed is:
 1. A method of cementing in a subterranean zonecomprising the steps of: preparing a lightweight cement compositioncomprising a coarse particulate hydraulic cement, an ultrafineparticulate hydraulic cement mixture of slag cement and a Portland orequivalent cement, fly ash, fumed silica, hollow glass spheres andsufficient water to form a slurry; placing said cement composition insaid subterranean zone; and allowing said cement composition to set. 2.The method of claim 1 wherein said coarse particulate hydraulic cementhas a particle size no greater than about 118 microns and a specificsurface area no less than about 2800 square centimeters per gram.
 3. Themethod of claim 1 wherein said coarse particulate hydraulic cement isAPI Class G Portland or the equivalent cement.
 4. The method of claim 1wherein said slag cement in said ultrafine cement mixture has a particlesize no greater than about 30 microns, a mean particle size of 6 micronsand a specific surface area no less than about 6000 centimeters pergram.
 5. The method of claim 1 wherein said Portland or equivalentcement in said ultrafine cement mixture has a particle size no greaterthan about 30 microns, a mean particle size of 6 microns and a specificsurface area no less than about 6000 centimeters per gram.
 6. The methodof claim 1 wherein said slag cement in said ultrafine cement mixture ispresent in said mixture in an amount of at least about 50% by weight ofsaid mixture.
 7. The method of claim 1 wherein said fly ash is ASTMClass F fly ash.
 8. The method of claim 1 wherein said ultrafine cementmixture of slag cement and a Portland or equivalent cement is present insaid cement composition in an amount in the range of from about 50% toabout 150% by weight of said coarse particulate hydraulic cementtherein.
 9. The method of claim 1 wherein said fly ash is ASTM Class Ffly ash.
 10. The method of claim 1 wherein said fumed silica is presentin said composition in an amount in the range of from about 20% to about60% by weight of said coarse particulate hydraulic cement therein. 11.The method of claim 1 wherein said hollow glass spheres are present insaid composition in an amount in the range of from about 21% to about310% by weight of said coarse particulate hydraulic cement therein. 12.The method of claim 1 wherein said water is selected from the groupconsisting of fresh water, saturated salt solutions and unsaturated saltsolutions.
 13. The method of claim 12 wherein said water is present insaid composition in an amount in the range of from about 128% to about400% by weight of said coarse particulate hydraulic cement therein. 14.The method of claim 1 wherein said composition further comprises a fluidloss control additive.
 15. The method of claim 1 wherein said fluid losscontrol additive is a mixture of a graft copolymer comprised of abackbone of lignin, lignite or salts thereof and a grafted pendant groupof 2-acrylamido-2-methylpropanesulfonic acid and a copolymer orcopolymer salt of N,N-dimethylacrylamide and2-acrylamido-2-methylpropanesulfonic acid.
 16. The method of claim 1wherein said fluid loss control additive is present in said compositionin an amount in the range of from about 0.2% to about 8% by weight ofsaid coarse particulate hydraulic cement in said composition.
 17. Themethod of claim 1 wherein said subterranean zone has a temperature inthe range of from about 45° F. to about 100° F. and said cementcomposition further comprises a cement composition set accelerator and acement composition dispersing agent.
 18. The method of claim 17 whereinsaid cement composition set accelerator is calcium chloride and ispresent in said composition in an amount in the range of from about 0.2%to about 12% by weight of said coarse particulate hydraulic cementtherein.
 19. The method of claim 1 wherein said cement compositiondispersing agent is the condensation product of acetone, formaldehydeand sodium sulfite and is present in said composition in an amount inthe range of from about 0.2% to about 8% by weight of said coarseparticulate hydraulic cement therein.
 20. The method of claim 1 whereinsaid subterranean zone has a temperature in the range of from about 100°F. to about 230° F. and said cement composition further comprises acement composition set accelerator.
 21. The method of claim 20 whereinsaid cement composition set accelerator is calcium chloride and ispresent in said composition in an amount in the range of from about 0.2%to about 12% by weight of said coarse particulate hydraulic cementcomposition.
 22. The method of claim 1 wherein said subterranean zonehas a temperature in the range of from about 230° F. to about 270° F.and said cement composition further comprises a cement composition setretarder and silica flour to prevent set cement strength retrogression.23. The method of claim 22 wherein said cement composition set retarderis selected from the group consisting of a copolymer of2-acrylamido-2-methylpropane sulfonic acid and acrylic acid and acopolymer of 2-acrylamido-2-methylpropane sulfonic acid and itaconicacid and is present in said composition in an amount in the range offrom about 0.2% to about 8% by weight of said coarse particulatehydraulic cement therein.
 24. The method of claim 22 wherein said silicaflour is present in said composition in an amount in the range of fromabout 20% to about 60% by weight of said coarse particulate hydrauliccement therein.
 25. A method of cementing in a subterranean zonecomprising the steps of: preparing a cement composition comprising: acoarse particulate hydraulic cement, an ultrafine particulate hydrauliccement mixture comprising slag cement and a Portland or equivalentcement present in an amount in the range of from about 50% to about 150%by weight of said coarse particulate hydraulic cement in saidcomposition, fly ash present in an amount in the range of from about 50%to about 150% by weight of said coarse particulate hydraulic cement insaid composition, fumed silica present in an amount in the range of fromabout 20% to about 60% by weight of said coarse particulate hydrauliccement in said composition, hollow glass spheres present in an amountsufficient to impart a density to said cement composition in the rangeof from about 9 to about 13 pounds per gallon, and water present in anamount sufficient to form a slurry; placing said cement composition insaid subterranean formation; and allowing said cement composition toset.
 26. The method of claim 25 wherein said coarse particulatehydraulic cement has a particle size no greater than about 118 micronsand a specific surface area no less than about 2800 square centimetersper gram.
 27. The method of claim 25 wherein said coarse particulatehydraulic cement is API Class G Portland or the equivalent cement. 28.The method of claim 25 wherein said slag cement in said ultrafine cementmixture has a particle size no greater than about 30 microns, a meanparticle size of 6 microns and a specific surface area no less thanabout 6000 centimeters per gram.
 29. The method of claim 25 wherein saidPortland or equivalent cement in said ultrafine cement mixture has aparticle size no greater than about 30 microns, a mean particle size of6 microns and a specific surface area no less than about 6000centimeters per gram.
 30. The method of claim 25 wherein said slagcement in said ultrafine cement mixture is present in said mixture in anamount of at least about 50% by weight of said mixture.
 31. The methodof claim 25 wherein said fly ash is ASTM Class F fly ash.
 32. The methodof claim 25 wherein said hollow glass spheres are present in an amountin the range of from about 21% to about 310% by weight of said coarseparticulate hydraulic cement in said composition.
 33. The method ofclaim 25 wherein said water is selected from the group consisting offresh water, saturated salt solutions and unsaturated salt solutions.34. The method of claim 33 wherein said water is present in an amount inthe range of from about 128% to about 400% by weight of said coarseparticulate hydraulic cement in said composition.
 35. The method ofclaim 25 which further comprises a fluid loss control additive.
 36. Themethod of claim 35 wherein said fluid loss control additive is a mixtureof a graft copolymer comprised of a backbone of lignin, lignite or saltsthereof and a grafted pendant group of2-acrylamido-2-methylpropanesulfonic acid and a copolymer or copolymersalt of N,N-dimethylacrylamide and 2-acrylamido-2-methylpropanesulfonicacid.
 37. The method of claim 36 wherein said fluid loss controladditive is present in an amount in the range of from about 0.2% toabout 8% by weight of said coarse particulate hydraulic cement in saidcomposition.
 38. The method of claim 25 which further comprises a cementcomposition set accelerator.
 39. The method of claim 38 wherein saidcement composition set accelerator is comprised of calcium chloride andis present in an amount in the range of from about 0.2% to about 12% byweight of said coarse particulate hydraulic cement in said composition.40. The method of claim 25 which further comprises a cement compositiondispersing agent.
 41. The method of claim 40 wherein said cementcomposition dispersing agent is the condensation product of acetone,formaldehyde and sodium sulfite and is present in an amount in the rangeof from about 0.2% to about 8% by weight of said coarse particulatehydraulic cement in said composition.
 42. The method of claim 25 whichfurther comprises a cement composition set retarder.
 43. The method ofclaim 42 wherein said cement composition set retarder is selected fromthe group consisting of a copolymer of 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid and a copolymer of2-acrylamido-2-methylpropane sulfonic acid and itaconic acid and ispresent in an amount in the range of from about 0.2% to about 8% byweight of said coarse particulate hydraulic cement in said composition.44. The method of claim 25 which further comprises silica flour toprevent set cement strength retrogression at elevated temperaturespresent in an amount in the range of from about 20% to about 60% byweight of said coarse particulate hydraulic cement in said composition.